In the API documentation where
“Collaboration Documents/secret”
has been used (e.g. https://api.fibery.io/?shell#update-entity-collection-field ), it seems it needs to be
“Collaboration~Documents/secret”
in order to work.
Believe this is due to something they said they are going to fix later.
When stuff are added automatically by Fibery, it uses ~ instead of spaces. When user creates it, uses spaces.
Many thanks to Martin for answer 
From our side - we can’t avoid tildes (at least for now) - so we promise to fix that part in the documentation 
Thanks for the heads up!
We’ve updated the docs to use Collaboration~Documents.
We’ve migrated most of our App and Type names to spaces but there are a few legacy exceptions. Collaboration~Documents is the most notable of them. If your workspace was created before 2020, there is a chance some other Apps still include ~ in their names.
When it comes to App/Type/Field names, the source of truth is your schema: Fibery API.
Great, thanks everyone 